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Q&A with Bob Polomski 23

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Extension Consumer Horticulturist, Clemson University

I have a hardy water lily that has been in the same pot for at least three years. The plant is now escaping from the pot. How should I go about dividing it? –A.R., Milton, NY

Answer: Hardy water lilies (Nymphaea cvv.) typically need to be divided every three years in areas colder than USDA Zone 7, and every one or two years in Zone 8 and warmer. A sign that a water lily is in need of division is small leaves and few flowers. Often the lily pads will be held above the water instead of lying flat on the surface.

The best time to divide is in spring, when the new growth is still halfway between the container and the water surface.

Lift the container out of the water and move it to a shaded location. Unpot the water lily onto a plastic sheet. Then wash off the soil from the tangle of rhizomes, shoots, and roots. Find the parent rhizome and growing tip and cut off a four- to six-inch section. You can repot this in the original container, using a heavy clay soil or an aquatic plant mix (calcined clay or arcillite, such as Schultz Aquatic Plant Soil). Width is more important than depth in potting up water lilies; the container need only be about six to eight inches deep, but the width of the pot should be about 14 inches for water lilies that occupy up to 12 square feet of pond area. More vigorous water lilies should be planted in an 18- to 20-inch-wide container.

Position the rhizome at a 45° angle, with the cut end close to the wall of the container. The growing point should be just above the soil surface. If you're going to topdress the pot with a layer of pea gravel, allow enough headroom so the growing point will be just above the surface. Add fertilizer tablets and then top it off with gravel.

Place the container in the water garden to a depth of six inches. At least two pads should float on the surface. After a few weeks, when the stems have elongated so all of the leaves are floating, lower the water lilies again, up to 16 inches deep.

If you want to make more water lilies, take the discarded portion and break off the sprouts or cut the parent rhizome into three- to six-inch-long sections containing one or two “eyes,” or growing points. Individually pot up the sprouts or rhizomes in wide, shallow containers.

Can you suggest some twisted, contorted-looking trees for my landscape? –S.L., Whittaker, MI

Answer: Plants with contorted stems invite attention, which makes them useful as accent plants or focal points. Probably the best known of these curious mutations is Harry Lauder's walking stick (Corylus avellana ‘Contorta’). Other deciduous plants that create enchanting winter silhouettes include selections of flowering quince (Chaenomeles speciosa ‘Contorta’), singleseed hawthorn (Crataegus monogyna ‘Flexuosa’), Japanese larch (Larix kaempferi ‘Diane’), mulberry (Morus bombycis ‘Unryu’), hardy orange (Poncirus trifoliata ‘Flying Dragon’), Fuji cherry (Prunus incisa ‘Kojo-no-mai’ or ‘Dance of the Butterflies’), and black locust (Robinia pseudoacacia ‘Tortuosa’).

There are several contorted willows to choose among, including Salix alba ‘Dart's Snake’, S. caprea ‘Kilmarnock’, S. xsepulcralis ‘Erythroflexuosa’ (golden curls), and S. matsudana ‘Tortuosa’.

A few contorted broadleaf evergreens to consider are selected forms of Japanese holly (Ilex crenata ‘Rocky Creek’), curly-leaf privet (Ligustrum japonicum ‘Coriaceum’), and cherry laurel (Prunus laurocerasus ‘Camelli-ifolia’). The last two have twisted leaves.

Finally, there are contorted evergreen conifers to be found among the cultivars of Hinoki cypress (Chamaecyparis obtusa ‘Torulosa’), Japanese cryptomeria (Cryp-tomeria japonica ‘Cristata’), Leyland cypress (xCupressocyparis leylandii ‘Contorta’), Hollywood juniper (Juniperus chinensis ‘Kaizuka’), and eastern arborvitae (Thuja occidentalis ‘Filiformis’).

I've had my ‘Brown Turkey’ fig for five years now, and it's been producing very well. Can you tell me when and how I'm supposed to prune it? –R.T., Piperton, TN

Answer: The fig is among the easiest of homegrown fruits. The plants can be trained either to a bush or a tree form; the below-freezing temperatures in regions where figs are marginally hardy often dictate a bush form. In late winter, before new growth begins and the buds begin to swell, prune out any dead or crossing branches. To eliminate overcrowding and to improve sunlight penetration, selectively thin one-third of the oldest stems at ground level. To encourage lateral branching, head back one-third to one-half of last year's wood at alternating heights to keep the fruit close to the ground.

For a tree form, create a vase-shaped or open-center canopy with three to five well-placed scaffold limbs. To keep the fruit within reach, make bench cuts by removing an upward-growing side branch at its point of origin on a horizontally oriented limb. Repeated bench cuts will “flatten” the canopy and encourage the fruiting limbs to spread sideways. Figs sucker quite easily, so you will need to remove wayward shoots close to the ground.

Any pruning before spring growth begins will result in the partial or complete loss of your breba or spring crop, which is produced on last year's wood. However, you can still enjoy your second or main crop, which is produced on the current season's shoots.

I heard that I need to inoculate my snap beans with some kind of bacteria to get a better harvest. Is this really necessary? –T.J., Springville, UT

Answer: If you haven't grown bean plants for several years in a particular location, inoculating the seeds will be beneficial. Beans and other legumes have the ability to acquire or “fix” nitrogen from the air and use it for growth. This is actually done by symbiotic Rhizobia bacteria that enter the root hairs of germinating seedlings and create nodules on the plant roots. Depending on the species of legume, nodules may range in size from a pinhead to a kernel of corn. The bacteria give the plant nitrogen and the legume provides the bacteria with carbohydrates.

Rhizobia are host specific. Snap beans, for example, need a different inoculant than peas. You can, however, buy combinations of inoculants that treat a variety of different legumes. Commercial inoculant is available in two forms: a black powder for coating the moistened seeds prior to sowing and a granular form for applying over the seeds in the furrow. These inoculants are perishable products; store them in a cool location (between 40 and 70' F) and out of direct sunlight. You can refrigerate the inoculant, but don't freeze it.

If you have grown a legume in recent years, there is little benefit to adding additional inoculant, since it is likely to be present in the soil. Also, the application of excess nitrogen inhibits the development of rhozobium nodules, so be careful not to overfertilize your inoculated legumes.

What is mushroom compost? My friends have told me that it's done wonders for their landscape. –C.L., Monroe, OR

Answer: Mushroom compost is a byproduct of mushroom cultivation. The crop is typically Agaricus bisporus—the white button mushroom and its brown strains, crimini and portobello—which accounts for 90% of commercial production in this country. After the mushrooms are harvested, the grower uses steam to elevate the temperature of the mushroom beds as high as 150°F for 8 to 24 hours to destroy any pathogens, insects, weed seeds, or other pests that may contaminate subsequent mushroom crops. Then the soil-like spent mushroom substrate is removed and marketed as mushroom soil, spent-mushroom compost, or simply mushroom compost.

The ingredients used to make mushroom compost vary by farm and by region, but may include wheat or rye straw, crushed corn cobs, sphagnum peat moss, horse manure, poultry manure, cottonseed, canola, or soybean meal, cocoa bean hulls, brewer's grain, grape crushings, synthetic nitrogen (such as urea or ammonium nitrate), potash, gypsum, or ground limestone.

When freshly removed from mushroom houses, mushroom compost has high levels of soluble salts. These can be harmful to germinating seeds and young plants. Weathering or curing uncovered piles of mushroom compost for six months, however, allows rain to leach out these salts. The mushroom compost can then be used as a topdressing on lawns, as a mulch, as a soil amendment, or wherever you use compost. H